The present invention relates generally to power transmission chains, which are widely used in the automotive industry and in industrial applications. More specifically, the present invention is directed to a power transmission system employing a plurality of parallel, adjacent chain assemblies which are connected by a retention bracket to form a single composite chain assembly.
In a power transmission application, an endless chain is wound around at least two sprockets, with the sprocket teeth engaging the chain. The sprockets are mounted on rotatable shafts. Rotation of a driving sprocket causes power transmission through the chain and consequent rotation of at least one driven sprocket. For instance, in an engine timing system, a chain provides power transmission between at least one driving sprocket positioned on a crankshaft and at least one driven sprocket positioned on a camshaft. Other automotive applications include, for instance, power transmission from a torque converter to a transmission and power transmission in the transfer case of a four wheel drive vehicle.
One type of power transmission chain is a silent chain, or a chain with links having inverted teeth and at least one toothed sprocket on each rotating shaft. Power transmission between each sprocket and the chain, and consequently between one sprocket and another sprocket, is provided by the meshing of the sprocket teeth with the inverted teeth of the chain.
Silent chains are formed by an arrangement of link plates in lateral and longitudinal directions. The links are interlaced and joined by pins. A typical chain is composed of inner links, which contact the teeth of a sprocket to provide power transmission, and guide links, which do not provide power transmission. Guide links are employed to maintain the chain on the center of the sprocket when the chain is wound around the sprocket. A row of link plates, arranged in the lateral direction, typically has a number of inner links combined with guide links in the center or at both edges of the row. Each inner link plate typically comprises a body portion having a pair of apertures for receiving the pins, and at least one depending toe shaped to fit between the teeth of the sprocket and provide power transmission therewith. U.S. Pat. No. 5,437,581, which is incorporated herein by reference, shows a silent chain known in the art.
Another type of power transmission chain is a roller chain, where the sprocket teeth are received between rollers or bushings on the pins which connect the link plates of the chain. As with silent chains, roller chains are formed by an arrangement of link plates interleaved in lateral and longitudinal directions. A typical roller chain consists of alternate inner links and outer links. The outer links, which are sometimes known as "pin" or "guide" links, consist of spaced link plates each having a pair of ends and an opening or aperture in each end. Pins are tightly received in the apertures of the outer links. The inner links, which are sometimes known as "bushing links," consist of spaced link plates each having a pair of ends and an opening or aperture in each end. Bushings are tightly received in the apertures. The bushings freely rotate about the pins, so that the inner links are pivotally connected to the outer links and able to articulate with respect to the outer links.
In some roller chain designs, rollers are provided on the bushings, and when the roller chain is wrapped around a sprocket, the teeth of the sprocket are received between the laterally spaced link plates and contact the longitudinally spaced rollers. These types of roller chains are sometimes called "true roller" chains. In other roller chain designs, referred to as "rollerless" chains, rollers are not deployed on the bushings, and, instead, the sprocket teeth are received between and contact the bushings themselves. Examples of roller chain are found in U.S. Pat. Nos. 4,186,617 and 5,226,856, which are both incorporated herein by reference.
A conventional chain drive may include a chain assembly of extended width in order to provide a chain of greater strength. Alternatively, two chain assemblies may be placed side-by-side between pairs of sprockets in order to achieve the power transmission results equivalent to that of a single extended width chain.
The most basic conventional engine timing system typically includes a single sprocket on the camshaft, with the crankshaft sprocket having one-half the number of teeth of the camshaft sprocket. Such a camshaft typically controls the valve train operation through hydraulic lifters and rocker arms connected to the valve stems. The chain can be of a narrow width in construction, such as shown in U.S. Pat. No. 4,758,210, which is incorporated herein by reference.
One challenge in the design of power transmission systems is the noise generated during the operation of chain drives. Noise is generated by a variety of sources, such as the impact of sprocket teeth on the contact surfaces of the chain at the onset of engagement. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket, and the mass of chain links contacting the sprocket at a particular moment or time increment.
The meshing impact sound is generally a periodic sound in chain drives. The impact sound is repeated with a frequency generally corresponding to the frequency of the chain meshing with the sprocket. This frequency is related to the number of teeth on the sprocket and the speed of the sprocket. The impact can produce sound having objectionable pure sonic tones.
Another cause of noise in chain drives is the chordal action of the chain and sprockets as the chain is driven about the sprockets. Chordal action occurs as the chain link initially engages the sprocket. The meshing of the chain and sprocket at the chain mesh frequency can cause a movement of the free chain or span (the part of the chain between the sprockets) in a direction perpendicular to the chain travel but in the same plane as the chain and sprockets (the "transverse" or "lateral" direction). This vibratory movement can also produce an objectionable pure sonic tone at the frequency of the chain mesh frequency or a derivative of it.
Many efforts have been made to minimize the objectionable pure sonic tones in chain drives by decreasing the noise level and pitch frequency distribution. The problem of noise reduction was addressed in U.S. Pat. No. 5,562,557, which is incorporated herein by reference, by various phasing relationships between the chain assembly and the sprockets. Phasing the chain and sprocket relationship can reduce the number of chain link teeth (or mass of chain) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket. Both of these phasing modifications, alone and in conjunction with the randomization of the chain and sprocket contacts, can alter the impact and chordal action generated sound patterns.
The phasing in U.S. Pat. No. 5,562,557 was achieved by modifying the chain assemblies as well as the sprockets. The modifications to the sprockets include the use of split sprockets which are phased by one-fourth, one-third, or one-half tooth space or pitch. The modifications to the chain assemblies include randomization or the use of single toe links in a single or dual chain assembly. To maintain the position of each chain assembly on its respective sprocket portion, the modifications include cutting a groove in the center of each sprocket portion, along which an inner guide link runs.
An inner guide link may also run along a groove between the sprocket portions. In U.S. Pat. No. 5,551,925, which is incorporated herein by reference, inner guide links are placed in a groove in the center between the phased sprocket portions. With inner guide links in the center groove, the guide links on the opposite or outer sides of the chain assemblies may be eliminated. Eliminating the guide links on either outer side of the chain assemblies allows a narrower phased chain and sprocket system.
While phasing of a silent chain drive reduces the level of noise generated by the impact and chordal action, such phased assembly has certain disadvantages. The phased assembly requires a groove on the sprocket that is expensive to cut. In addition, manufacture and assembly of the chain systems are difficult, and the chains must be of a matched set.
The present invention addresses these problems by providing a phased chain assembly with a retention bracket to hold the chains together. In this manner, the center groove of the sprocket is eliminated and the chain is assembled into a single composite assembly of the two chains.
Retention brackets have been used to prevent transverse movement of the pivot means in chain assemblies of the prior art. In U.S. Pat. No. 4,738,654, which is incorporated herein by reference, a retention bracket, or retaining clip, is used to retain the pivot means or joint members in the apertures of the links of the chain assembly. The retaining clips include a horizontal back portion that transversely spans the links of the chain assembly, and depending arms joined to each end of the back that engage either a pivot means or an outer link surface.
However, the device disclosed in U.S. Pat. No. 4,738,654 does not employ a retention bracket to maintain the relative longitudinal positions of one or more separate chains. Moreover, the device disclosed in U.S. No. Pat. No. 4,738,654 is not suitable for use with a phased sprocket system, wherein the chain portion attached to one arm of the retaining clip engages a sprocket before the chain portion attached to the other arm of the retaining clip. In contrast, the present invention is directed to maintaining the relative longitudinal positions of two or more chains, including chains in a phased relationship.